When water for polymerization use is used in each of production plants for various polymers and copolymers, the water for polymerization use is generally introduced into a polymerization kettle through a transfer pipe.
Industrial water, pure water (water in which the amount of impurities has been reduced by performing a treatment, such as a deionization treatment, a distillation treatment, or a reverse osmosis membrane treatment), or the like is generally used as the water for polymerization use. In particular, in a production plant requiring water for polymerization use containing a small amount of impurities, first, the water for polymerization use containing a small amount of impurities is prepared by a pure water production step (see, for example, Patent Literature 1).
However, even when similar kinds of pure water are used, depending on the kind of polymer or copolymer to be produced, polymerization reproducibility may be high, or the polymerization reproducibility may be low, and hence stable production of a high-quality product (copolymer) may be hindered.